Coupling and method for detecting heart rate

ABSTRACT

The invention relates to a coupling and method in a heart-rate measuring apparatus. The coupling in the heart-rate measuring apparatus ( 10 ) comprises means ( 1, 2, 3, 4, 5 ) for measuring heart rate and means for wireless data transmission ( 7 ). According to the invention, the heart-rate measuring device ( 10 ) comprises means ( 1, 2, 3, 4, 5 ) implemented by analog electronics for defining the maximum value of the heart-rate signal, or a parameter proportional to it.

The invention relates to a coupling according to the preamble of claim 1for detecting heart rate.

The invention also relates to a method for detecting heart rate.

According to the prior art, U.S. Pat. No. 5,876,350 Lo et al. disclosesthe filtering of a pulse signal, after AD conversion. The pulse signalthus contains disturbance in the analog stage and the digital signalrequires heavy processing for the required data to be recovered from thesignal for further processing.

U.S. patent application 200610094969 discloses a PQRST wave and depictsthe environment, to which our invention relates.

U.S. Pat. No. 5,810,722 discloses digital ways of filtering a heart-ratesignal.

The invention is intended to eliminate the drawbacks of the prior artand create an entirely new type of coupling and method for detecting apulse.

The invention is based on using analog electronics to process theheart-rate signal to remove interference from it before it is forwardedor taken to the processor.

Thus, according to one preferred embodiment of the invention, themaximum value of the heart-rate signal is sought, using analogelectronic means, from the electrical signal induced by the heart.

According to a second preferred embodiment, the detection of the maximumis confirmed with the aid of an analogically defined time derivative ofthe descending edge of the signal.

Further, according to a third preferred embodiment, the time stamp ofthe maximum is obtained from the descending edge after the maximum, forexample, by sending an interrupt to a microcontroller.

According to a fourth preferred embodiment of the invention, thedetected maximum is accepted as the moment of the heartbeat, if a newmaximum is not detected after the detection of the maximum, during aperiod of a predefined number of milliseconds x (x being approx.200-250).

According to a fifth preferred embodiment of the invention, afteracceptance of the maximum, the new maximum should be at least ‘previousmaximum−y’ mV (y being approx. 0.5).

According to a sixth preferred embodiment of the invention, if a newmaximum is not detected during the maximum heart-rate interval (e.g., 2seconds), the reference level is reset to its minimum value.

More specifically, the coupling according to the invention ischaracterized by what is stated in the characterizing portion of claim1.

The method according to the invention is characterized, for its part, bywhat is stated in the characterizing portion of claim 11.

Considerable advantages are achieved with the aid of the invention.

With the aid of the invention, A/D conversion can be entirely avoided inthe heart-rate transmitter. As a signal with less interference isobtained from the analog part of the heart-rate transmitter, in someembodiments of the invention the signal processing of the digital sideof the heart-rate belt can be significantly simplified. Typically, awristop computer will not require any separate modifications in order toimplement the invention.

Known heart-rate measuring electronics using a fixed triggering voltagemay cause a situation, in which the voltage caused by a contraction ofthe heart muscle of a person in the measurement range is small, theperson will not be able to measure his heart rate using the belt inquestion. On the other hand, the solution according to the inventionadapts substantially to the measured signal.

In the following, the invention is described with the aid of theembodiments according to the accompanying drawings.

FIG. 1 shows a schematic block diagram of the environment according tothe invention.

FIG. 2 shows a circuit diagram of a preferred embodiment of theinvention.

FIG. 3 shows a circuit diagram of another preferred embodiment of theinvention.

FIG. 4 shows schematically one application of the invention.

FIG. 5 shows a circuit diagram of one application according to theinvention.

According to FIG. 1, the invention relates to an environment, in whichby means of the heart-rate measuring apparatus such as a heart-rate belt10 or similar, heart-rate data is transmitted wirelessly to a receiverdevice 20, for example, a wristop computer. The heart-rate measuringdevice 10 thus contains means for measuring heart rate, such asmeasuring electrodes and their related electronics, and means forforwarding the heart-rate data wirelessly. The receiver apparatus 20,for its part, comprises means for receiving heart-rate data over awireless transmission channel, as well as means for analysing thereceived heart-rate data and/or displaying it and/or for displaying theresult data. The receiver apparatus 20 can also act solely as a remotedisplay for the heart-rate belt.

The central ideas of the invention is to refine the heart-rate signal inan analog form in the heart-rate transmitter 10, to be clean enough forit to be connected directly to the microcontroller of the heart-ratebelt 10, or even to be transmitted in an analog form to the receiverunit 20. Thus, digital further processing in the receiver unit 20 can bemade as simple as possible and, on the other hand, the heart-rate belt10 containing the transmitter can also be made simple, economical, andreliable.

The circuits shown in FIGS. 2 and 3 are thus located in block 10 of FIG.1.

According to FIG. 2, the detection of the maximum is implemented inblock 1. Block 1 uses a comparator U6 to compare the input signalarriving at its first input 3 with the recorded previous maximum, whichis obtained from the output of block 2 and is fed to the second input 4of the comparator U6. When the input signal is greater than the previousmaximum, the pulse is brought to the controller from the output 1 of thecomparator U6.

In block 2, the recording of the maximum is implemented with the aid ofa transistor Q1 and a capacitor C37. This block stores the maximum valueof the input signal produced by the previous block 1. As stated above,the stored maximum value acts as a reference for the comparator U6 ofblock 1 and connects this to the second input.

Block 1 and block 2 combined form a peak detector.

In block 3, the calculation of the maximum is implemented with the aidof a transistor Q2. The longer a zero pulse is connected to the base oftransistor Q2, the more the recorded maximum value will drop off. Thisallows the reference voltage of block 1 to be regulated by altering thelength of the zero pulse. The recorded maximum value is calculated atregular intervals. The microcontroller (not shown) can alter theinterval as required. When the reference voltage of block 3 is leftabove the zero level, in an environment with interference no new pulsewill come immediately to the microcontroller.

If new maximum values do not appear within a set time, the maximum valuestored in block 2 can be reset using a long zero pulse.

Block 4 acts as a zero detector. The voltage set by the microcontrolleracts as a reference for the comparator U1. Here, the voltage in questionis marked as half of the operating voltage, but this need notnecessarily be the case. The pulse for the controller from block 4 isobtained from the RS edge descending from the QRS complex.

The pulse succeeding the maximum value of the input signal (the pulsefrom block 1 to the microcontroller) from block 4 (less than thereference level set by the microcontroller) represents the QRS complex.

The time stamp is recorded by the microcontroller from the pulse of bothblock 1 and block 4. The pulse caused by the QRS complex from block 4comes in the known time window after the pulse coming from block 1. Ifit does not, it is a question of a disturbance.

Block 5 of FIG. 3 is a microcontroller. The microcontroller sets thedefault value for the reference voltage of block 4. If pulses occur fromblocks 1 and 4 in the set time window, the time stamp of the heartbeatis recorded. The maximum voltage recorded in block 2 after the timewindow is calculated by block 3.

The length of the pulse going to block 3 and the reference voltage ofblock 4 are changed as required. After this, a new time window starts.

Block 6 is a memory. If the application records information,non-volatile memory (EPROM or flash) is used. Block 7 is a data link, bymeans of which the application forwards the heart-rate data wirelessly,for example, to a wristop computer.

According to FIG. 4, the invention can be applied in connection withcycling, among other things, in which the bicycle 40 compriseshandlebars 41 and brake levers 42 attached to them. In addition, thebicycle has normally a front gear changer 44 and a rear gear changer 45.The front gear changer 44 guides the chain to the desired frontchainwheel 47 and correspondingly the rear gear changer 45 and 20 isused to guide the chain 46 to the desired rear sprocket. A measuringdevice 70 can be fitted in connection with the rear wheel 49 supportedby the rear forks 71 and 60, for measuring the tension of the chain, oralternatively the device 70 can be used for wireless gear-changing.Correspondingly, a speedometer sensor 81, which receives its signal froma magnetic piece attached to a spoke in the front wheel 82, can befitted in connection with the front wheel 82.

Thus, according to the invention, the devices in connection with thewristop computer 43 acting as the receiver device, in this case theheart-rate belt 10, the device 70, and/or the speedometer sensor 81 areused to form, with the aid of the analog electronics, a definition ofthe signal's maximum value, or a parameter proportional to it, beforethe signal is transmitted to be digitized, or before its transmission tothe wristop computer 43. In a cycling application, the wristop computer43 corresponding to the receiver 20 of FIG. 1 can be able to be attachedto the handlebars 41, or alternatively the receiver can be a purecycling computer attachable to the handlebars with a quick-release lock.

According to FIG. 5, the means implemented by analog technology forconfirming the detection of a maximum with the aid of a time derivativeof the descending edge of the signal can be implemented, for example, bya differentiator 50, which is connected between the input IN and themicrocontroller of FIG. 2 (e.g., FIG. 3, block 5). In practice, thedifferentiator is formed of an operational amplifier 51, the output andnegative input of which are connected as feedback, by a resistor R11 anda capacitor C11 connected in parallel. The positive terminal of theoperational amplifier 51 is connected to a constant voltage, in thiscase to half of the operating voltage. Between the negative input andinput IM of the operational amplifier 51, a resistor R10 and a capacitorC10 are further connected in series.

According to the invention, once a heartbeat has been detected ortriggered, it can be forwarded wirelessly, for example, equipped withidentifier information. Alternatively, a set of heartbeat-related timestamps, which have been produced with the aid of the invention, can betransmitted.

The form of transmission can also be such that the hear-rate/minutevalue is calculated and forwarded. The manner of transmission of thecalculated value requires at least some detected heartbeats to berecorded in the heart-rate belt, in order to form a transmission signal.The heart-rate data need not always be transmitted to the display deviceor the receiver device during the performance, but can be collected in aheart-rate belt, wristop device, or cycle computer for later use.

The invention can also be applied in a heart-rate belt equipped withmemory, the contents of which memory can be also downloaded wirelesslyto a PC, or by wired transmission for later hear-rate-based analyses.

Various analyses, for example, of energy consumption, can be calculatedin real time or afterwards from any of the devices described.

1. Coupling in a heart-rate measuring apparatus (10), which comprisesmeans for measuring heart rate (1, 2, 3, 4, 5) and means for wirelessdata transmission (7), characterized in that the heart-rate measuringdevice (10) comprises means (1, 2, 3, 4, 5) implemented by analogelectronics, for defining the maximum value of the heart-rate signal ora parameter proportional to it.
 2. Coupling according to claim 1,characterized in that the means (1, 2, 3, 4, 5) implemented using analogelectronics, for defining the maximum value of the heart-rate signal ora parameter proportional to it, are connected directly to amicrocontroller (5) of the heart-rate measuring device (10).
 3. Couplingaccording to claim 1 or 2, characterized in that it comprises meansimplemented by analog technology for confirming the detection of amaximum, with the aid of a time derivative of the descending edge of thesignal.
 4. Coupling according to claim 1, characterized in that itcomprises means (1, 4) for acquiring a time stamp of a maximum from thedescending edge after the maximum, for example, by sending an interruptto the microcontroller (5).
 5. Coupling according to claim 1,characterized in that it comprises means for accepting a detectedmaximum as a heartbeat moment, if a new maximum is not detected afterthe detection of the maximum during a period of a predefined number ofmilliseconds x (x being approx. 200-250).
 6. Coupling according to claim1, characterized in that it comprises means for accepting a maximum on acondition, by which the new maximum should be at least ‘previousmaximum−y’ mV, where y is approx. 0.5.
 7. Coupling according to claim 1,characterized in that it comprises means for returning (resetting) thereference level to its minimum value, if a new maximum is not detectedduring the maximum heartbeat interval (2 seconds).
 8. Coupling accordingto claim 1, characterized in that the heart-rate measuring device (10)comprises means for transmitting heart-rate data equipped withidentifier information.
 9. Coupling according to claim 1, characterizedin that the heart-rate measuring device (10) comprises means fortransmitting time stamps relating to the heartbeats.
 10. Couplingaccording to claim 1, characterized in that the heart-rate measuringdevice (10) comprises a memory.
 11. Method in a heart-rate measuringapparatus, in which the heart rate is measured by a heart-rate measuringdevice (10), and the measured heart-rate data is transmitted wirelesslyto a second apparatus (20) for analysis, or display, or display of theanalysis results, characterized in that a definition of the maximumvalue of the heart-rate signal, or a parameter proportional to it, isimplemented in the heart-rate measuring device (10) by means of analogelectronics (1, 2, 3, 4, 5).
 12. Method according to claim 11,characterized in that the means (1, 2, 3, 4, 5) implemented by analogelectronics, for defining the maximum value of the heart-rate signal, ora parameter proportional to it, are connected directly to amicrocontroller (5) of the heart-rate measuring device (10).
 13. Methodaccording to claim 11 or 12, characterized in that the detection of amaximum is confirmed by analog technology, with the aid of a timederivative of the descending edge of the signal.
 14. Method according toclaim 11, characterized in that the time stamp of a maximum is acquiredfrom a descending edge after the maximum, for example, by sending aninterrupt to the microcontroller.
 15. Method according to claim 11,characterized in that the detected maximum is accepted as the moment ofa heartbeat, if, after the detection of the maximum, a new maximum isnot detected during a period of a predefined number of milliseconds x (xbeing approx. 200-250).
 16. Method according to claim 1, characterizedin that the maximum is accepted on a condition, by which the new maximumshould be at least ‘previous maximum−y’ mV, where y is approx. 0.5. 17.Method according to claim 1, characterized in that the reference levelis returned (reset) to its minimum value, if a new maximum is notdetected during the maximum heartbeat interval (2 seconds).
 18. Methodaccording to claim 1, characterized in that the heart-rate data istransmitted from the heart-rate measuring device (10) equipped withidentifier information.
 19. Method according to claim 1, characterizedin that the heart-rate data is transmitted from the heart-rate measuringdevice (10) as time stamps relating to the heartbeats.
 20. Methodaccording to claim 1, characterized in that information is recorded inthe heart-rate measuring device (10).
 21. Heart-rate measuring system,which comprises a heart-rate measuring device (10), which includes meansfor measuring heart rate and means for wirelessly forwarding heart-ratedata, and a receiver apparatus (20), which comprises means for receivingheart-rate data over a wireless transmission channel, as well as meansfor analysing or displaying the received heart-rate data, or fordisplaying the analysis results, characterized in that the heart-ratemeasuring device (10) comprises means (1, 2, 3, 4, 5), implemented byanalog electronics, for defining the maximum value of the heart-ratesignal, or a parameter proportional to it.
 22. System according to claim21, characterized in that it comprises means according to any of thedevice claims.